1. Field of the Invention
The present invention relates to substrates, duplexers, substrate modules and manufacturing methods therefor, and more specifically relates to a substrate on which a high-frequency-side filter component and a low-frequency-side filter component are mounted, and to a duplexer and a substrate module.
2. Description of the Related Art
A branching filter described in Japanese Unexamined Patent Application Publication No. 2009-290606 is a known example of a duplexer of the related art. The duplexer described in Japanese Unexamined Patent Application Publication No. 2009-290606 is formed by mounting a piezoelectric substrate, which has a transmission surface acoustic wave filter and a reception surface acoustic wave filter provided on one main surface thereof, on a circuit board. This kind of circuit board, for example, is mounted on a motherboard of a wireless communication device.
In the branching filter described in Japanese Unexamined Patent Application Publication No. 2009-290606, inductor patterns for matching the transmission surface acoustic wave filter and the reception surface acoustic wave filter are built into the circuit board. As a result, when wiring lines such as inductor patterns are provided inside the circuit board, a transmission signal path and a reception signal path are close to each other and liable to become electromagnetically coupled. As a result, there is a risk of a transmission high frequency signal entering the reception signal path and thus the isolation characteristics of transmission and reception being degraded.